n2o and octane

**pocheasy** · 12-02-2007, 04:43 AM

edit:damn I must of ben half sleeping still, cant edit the title but this is about n2o and octane.

some fool I know is claiming he knocked off a half second in the 1/4 simply by switching to 106 octane while spraying a 200 shot. Im def no expert on nitrous but this doesn't sound right to me.. octane doesn't help out at all with nitrous does it? or atleast not by that much right? could some one get technical about it please?

**Olde Skoole** · 12-02-2007, 06:12 AM

Raising the Octane level allowed him to run more advance in the timing which helped the engine make more power and consequently shaved a half second off ET.

**mrr23** · 12-03-2007, 05:42 PM

or, maybe he was detonating and needed the additional octane to stop it from happening which resulted in his lower ET. i run 93 octane in my 408 motor with a 250 shot with no knock.

BTW, i fixed your title.

**pocheasy** · 12-05-2007, 04:33 AM

thanks for the replys but I still think im gettin bullshited here. his c/r is only 8:1 and when I asked if he was running any advanced timming he just laughed. 8:1, 200shot and 106octane? the octane alone cant take a half second off his ET can it?

**Hobbesnmina2001** · 12-05-2007, 05:22 AM

Sorry to butt in here, newbie to the board.
Like the others say depends on what the conditions where before the octane raise.
Here is a slightly different power adder a blower and my friends have a Henry with a 355 SBC 6-71 they used to run NOS. Anyway they where running 11 # boost on gas and switched to E85 no other changes and their et dropped by 2 tenths and their mPH went up by 6!!
The way fuels burn involves a lot more then octane. Octane rating is a measure of the amount a fuel mixture may be compressed before self ignition. High Octane fuels vary in their make up and two different fuels of similar octanes can make different power. A few different examples are aviation gas, race gas, alcohols, LPG. These all have naturally high octanes but they burn at different rates and the old aviation gas for example was cheap and high octane but was meant for slow rpm motors (2400-3200 rpm) in a high winding engine would not perform like a good race gas which is formulated with high octane but faster burning hydrocarbons.
Not trying to be a know it all, just inserting some food for thought.

Carlos

**Olde Skoole** · 12-06-2007, 06:27 AM

high-octane fuels burn slower than low-octane fuels, so it only makes sense to run the lowest octane that the motor will accept.
Now watch, some fool is gonna come on here and tell me that high-octane fuel makes more power.......WRONG, high-octane fuels allow the end-user to use more static compression and more advance in the timing which all help the engine produce more power, remember that when we raise the octane rating we are slowing down the flame-front or combustion process.
There are plenty of other factors that come into play when designing a high-compression engine to run on the lowest possible octane level.....cylinder head material; aluminum dissipates heat quicker than cast-iron and will usually allow at least a 1/2 point more compression....combustion chamber design is a often overlooked factor; spark plug heat range; air/fuel ratio, without delving too deep here any technician worth his salt knows that a "stoichiometric" air/fuel ratio of gasoline is 14.7:1 and peformance engines enjoy a slightly richer mixture of 12.7:1.
Ethanol and Methanol added to gasoline will effectively richen the mixture with no other adjustments.....remember the methanol discussion.
The squish-band is the major player IMHO; the squish-band is the area between the top of the piston and deck surface of the cylinder head, we strive to minimize the squish-band by using the thinnest possible head-gasket and/or decking the block until the the top of the piston is above the deck of the block at TDC..
Hypothetical situation; the compressed thickness of a factory LS1 head gasket is .030", you want to have at least .010" piston/head clearance to compensate for rod-stretch (yes, rods stretch at high-rpm) so we need the top of the piston to extend .020" above the deck of the block to give us the required .010" squish-band...............my brain is tired now, bye.

**Hobbesnmina2001** · 12-09-2007, 07:28 PM

Old Skoole, you bring up some good points but unfortunately high octane and flame travel are not linear or go hand in hand necessarily.
There are high Octane fuels that will burn quicker then others. If you take an ounce of high octane race gas like VP c12 and spread it on the cement along with an ounce of regular 87 octane, and an ounce of aviation gas the C12 will evaporate quicker. Octane is the ability to withstand higher pressure not evaparotion rate. Natural gas and LPG (uncondensables like methane, ethane, and propane) have a high octane rating and one could say a high evaporation rate since they non condensables but are still a hydrocarbon. Not trying to be smart its just the way things are. A molecules ability to be "squeezed" more (Octane rating) is based more on the molecular structure.
There are times when your example is correct like the difference between benzene, toluene, and xylene, all high octane (2 points apart), of the three toluene has the best characteristics for a race fuel and as a blending agent is loved as such.

Good day

Carlos

**Olde Skoole** · 12-10-2007, 12:26 PM

Old Skoole, you bring up some good points but unfortunately high octane and flame travel are not linear or go hand in hand necessarily.

True..

There are high Octane fuels that will burn quicker then others.

True, but for the most part the higher the octane the slower the combustion process...

If you take an ounce of high octane race gas like VP c12 and spread it on the cement along with an ounce of regular 87 octane, and an ounce of aviation gas the C12 will evaporate quicker.

That's a interesting analogy, however i fail to see how it relates to a air/fuel mixture under pressure...

Octane is the ability to withstand higher pressure not evaporation rate.

Octane rating is detonation resistance...i still fail to understand your inclusion of evaporation rate into the discussion, but i will research it...

thank-you for a intelligent and informative reply, i look forward to more discussions with you..
My knowledge is comprehensive yet dated and i do admit to not knowing all the intricasies of the LS model engines, however much as things change they stay the same...
I'm not sold on the 3rd Gen engine as the Messiah,
the 1st Gen family is where my heart is at.

**Hobbesnmina2001** · 12-10-2007, 07:19 PM

Old Skoole, thank you for the kind words, I am new to the LS1 and newer computer tech cars. I worked for 17 years in a couple of refineries. Being a car nut at my first refinery I became good friends with the guy that ran the knock machine!!

We ran tests for me on octane boosters and I picked his brain every chance I got, I don't pass myself off as a know it all but feel I do have a handle on some of this stuff. If you are interested I would recommend Jeff Hartmans book on High Performance Fuels and Lubricants its pretty good. He is for the most part accurate although I remember him being off on a couple of refinery points but its not a big deal.
Part of my point is that often people think hydrocarbons are linear in their characteristics and I wanted to point out that high octane fuels can be light ends or heavier in make up. Also just because a fuel is high octane it may burn slower or quicker then another hydrocarbon.
Evaporation rate does play into power making ability due to the fact that the easier a fuel evaporates the easier it can mix with air and burn. I do agree with you that in general using more octane then necessary only tends to burn the pocket book. I was surprised a while ago when a magazine during a pump gas engine dyno run also ran a final test using race fuel over the pump fuel and made more power. The race fuels power making ability was attributed to the faster evaporation rate of the race fuel. If memory serves me correctly the writer and tester was David Vizard a well respected power making technical guru.
I do not work for VP Race fuels and I am a believer in that smaller companies become successful by making better quality products.
A Pro racer and engine builder friend told me he has seen as much as 50 HP on the dyno in similar octane fuels on 800-850 hp enines. Whats the difference? Its the hydrocarbons chosen and blended into that mix. A large oil company will look around and give an octane range but they will use what components they have on hand and premium hydrocarbons that can go for more money may not make it into the batch. My ex employer use to make race fuel at our refinery for a top Indy and Nascar racer they sponsored and I saw this personally. A smaller company like VP does not have refining capacity they buy the individual components and mix their own. Its ironic but as a racer you will usually get a more consistent product from a smaller company because they are buying the same components all the time, at least they do if they want to make a consistent product, VP is one such company.

Take care

Carlos